Apparatus and method for forming plastic preforms into plastic containers with controlled recycling of compressed air

The present invention relates to an apparatus and a method for forming plastic preforms into plastic containers. In the area of the beverage manufacturing industry, it has long been known that heated plastic preforms are formed into plastic containers and expanded in particular. For this purpose, the plastic preforms are expanded into the containers inside blow molds using a flowable medium, usually pressurized air (but sometimes also by means of liquids). Typical machines that perform these processes are stretch blow molding machines.

In prior art stretch blow molding machines, different pressure levels are used for forming containers, which are brought into flow communication with the container by means of a valve arrangement and particularly a valve block. Prior art methods with two or three pressure stages in the pressure build-up are known. However, in the applicant's internal prior art, configurations with four pressure stages are already being tested. Air is usually used as the pressurized medium, but other gaseous fluids and also liquids, such as the beverage to be filled, can also be used.

A pressure build-up phase sometimes has four pressure stages. The individual pressure levels are set by the machine operator in the prior art. These pressure stages, for example four, are applied to the container one after the other in ascending order via the valves located on a valve unit such as a valve block.

After the highest pressure is held for a determined time, the recycling phase of the process follows. In the following, the recycling phase is understood to be the phase in which the flowable medium (particularly from the container to be expanded) is returned to the individual pressure reservoirs (which may be annular channels, for example).

During the recycling phase, the valves of the individual pressure stages are advantageously opened one after the other in descending order. The pressure prevailing in the vessel is relieved to the respective pressure level of the individual stages (and in particular into the respective pressure reservoirs), wherein air mass flows from the vessel into a pressure reservoir.

A valve opening time of the valves during the recycling phase determines the air mass which is recycled. This assumes a pressure gradient between the container and the pressure reservoir of the individual stages. If the individual valves are open long enough for complete pressure equalization to occur between the container and the respective pressure reservoir, a longer valve opening time will not result in a higher recycled mass. In the prior art, the valve opening times are controlled in such a manner that the pressure set by the operator in the pressure reservoir is reached as far as possible.

In the prior art, the starting times of the individual recycling cycles are set on the basis of the unloading time of a container, which is characteristic for the respective machine, using the valve opening times calculated by a regulating device.

A regulating deviation detected by the regulating device is the difference between a set pressure and the actual pressure of a pressure reservoir of the respective pressure stage. In the applicant's internal prior art, some parameters of the blowing curve are set by an operator and some are determined by the machine itself.

Of particular importance for the compressed air consumption of the respective system is the pressure in the container at the respective unloading time, since the pressure consumption per container is calculated from the unloading pressure, the container volume and the dead space of the station.

A disadvantage of the current approach is the intended user input of the intermediate blowing pressures by the user because this allows a recycling control unit to find an optimum for this input at best. This means that the respective reservoir pressures are reached, but a relief pressure is far above the lowest possible relief pressure. The lowest possible relief pressure corresponds to the pressure of the lowest pressure stage in the pressure build-up.

Another disadvantage is the recycling start times, which depend on the valve opening times. If one feeds back into the pressure reservoir at an inopportune time, for example when the reservoir pressure is at its highest, the recycling potential is reduced. An additional disadvantage of the current approach is that the characteristics of air extraction from the reservoir in the ascending branch (pressure build-up phase) are not taken into account during recycling and thus recycling potential remains unused.

The object of the present invention is therefore to provide such apparatuses and methods more energy efficient. In particular, the object is to improve the efficiency gains that can be achieved through compressed air recycling.

In a method according to the invention for forming plastic preforms into plastic containers, a plastic preform (and preferably a plurality of plastic preforms) is expanded into the plastic container by being acted upon by a flowable and in particular gaseous medium and in particular air, wherein the flowable medium is stored under a first pressure in a first pressure reservoir and is stored under a second pressure which is higher than the first pressure in a second pressure reservoir, and wherein the plastic preform is acted upon by a first blowing pressure via a flow connection between the first pressure reservoir and the plastic preform and is acted upon by the second blowing pressure via a flow connection between the second pressure reservoir and the plastic preform. Preferably, the second blowing pressure is applied after the first blowing pressure.

Furthermore, at least intermittently, flowable medium (particularly pressurized air) is returned (particularly from the container) to the first pressure reservoir, wherein first values characteristic of the application of the flowable medium to the plastic preforms are preferably predetermined.

In a first embodiment according to the invention, taking into account the first values, second values are determined which are characteristic of a time or period (and in particular a starting time) of the return of the flowable medium into the first pressure reservoir.

In a second method according to the invention, a point in time and/or period of time for returning the flowable medium (and in particular a starting point in time) to the reservoir is selected and/or determined as a function of a point in time and/or period of time for applying the flowable medium to the plastic preform. In a further method according to the invention, at least one point in time and/or period of time (and in particular a start time for a return to the first pressure reservoir) is determined as a function of a point in time and/or period of time (and in particular a start time) that is characteristic of the application of pressure from a pressure reservoir to the plastic preform.

Furthermore, it would also be conceivable to apply the methods of the invention described here cumulatively. It would also be possible to use different methods for different pressure levels and/or pressure reservoirs, approximately for an intermediate pressure Pi the first of the methods described above and for an intermediate pressure Pi+ the second method.

Preferably, at least two of the start times are determined. Particularly preferably, the starting times for the return of the flowable medium are determined in at least one pressure reservoir, which is used for the receptacle of an intermediate blowing pressure.

Particularly preferably, said first values are at least partially and preferably completely predetermined by a user. However, it would also be possible that these first mentioned values are calculated by a machine controller. These values can, for example, be determined as a function of the container to be produced. It would also be conceivable for these values to be determined and/or ascertained as a function of the plastic preform to be expanded.

Particularly preferably, the plastic preform is transported along a predetermined transport path while being exposed to the flowable medium. Particularly preferably, a plurality of plastic preforms are at least partially simultaneously (or in at least partially overlapping time periods) exposed to the flowable medium in order to be expanded.

Through the two procedures according to the invention, an increase in efficiency can be achieved with regard to the blowing air. In particular, the (start) times at which the recycling of air, hereinafter referred to as recycling, is performed can be determined in this manner.

In a preferred method, the first values are selected from a group of values comprising a magnitude of a first pressure (in particular a pre-blow pressure P), a magnitude of a second pressure (in particular a first intermediate blow pressure Pi), which is preferably higher than the pre-blow pressure), a magnitude of a third pressure (in particular a second intermediate blow pressure Pi+) which is preferably higher than the first intermediate blowing pressure Pi), a magnitude of a fourth pressure (in particular a final blowing pressure P), a point in time for the start of pressurization with the first pressure, a point in time for the start of pressurization with the second pressure, a point in time for the start of pressurization with the third pressure a time for the start of the application of the fourth pressure, a duration of the application of the first pressure, a duration of the application of the second pressure, a duration of the application of the third pressure, a duration of the application of the fourth pressure, a time for the end of the application of the first pressure, a time of termination of the application of the second pressure, a time of termination of the application of the third pressure, a time of termination of the application of the fourth pressure, the time of the start of a discharge of (residual) pressure into the environment (exhaust) and similar.

Particularly preferably, these times are controlled by the switching times of valves which are arranged at the forming station and preferably each forming station of a plurality of forming stations. The individual time durations or also the time points can be controlled by means of corresponding valves or their switching times. Offsets can also be added, which take into account a reaction time of the valves.

Furthermore, values can also be controlled, such as a pressure level within the pressure reservoirs. Particularly preferred is at least one pressure reservoir and preferably several pressure reservoirs are designed as annular channels. Preferably, the pressure reservoirs are arranged on a movable carrier, on which the forming stations are also preferably arranged.

In a further preferred method, the plastic preforms are transported along a predetermined (particularly circular) transport path, and preferably expansion takes place during this transport. Preferably, the plastic preforms are placed in blow molds and subsequently exposed to the flowable medium. It is possible to open the blow molds, insert the plastic preforms into them and then close the blow molds again. Particularly preferably, the plastic preforms are stretched in their longitudinal direction. This is done, particularly preferably, by inserting a stretching bar into the interior of the plastic preforms. Particularly preferably, this stretching of the plastic preforms in their stretching direction or in their longitudinal direction takes place at least partially simultaneously with the application of different pressures.

Particularly preferably, the movement of the stretching bar is also controlled taking into account at least one start time for pressurization of the plastic preform. In this manner, the forming process can be optimized even further.

Particularly preferably, the plastic preform and preferably the plastic preforms are subjected to at least three and preferably at least four different pressures or pressure stages for its or their expansion. Particularly preferably, recycling or recirculation of the gaseous medium takes place in at least two pressure reservoirs, preferably in at least three pressure reservoirs.

Particularly preferably, an expansion pressure is determined before and/or during pressurization of the plastic preform and/or a recycling pressure is determined during recirculation of the flowable medium into a pressure reservoir. Particularly preferably, a pressure of the gaseous medium inside the container is determined at least intermittently and preferably continuously.

Particularly preferably, a pressure of the flowable medium is determined at least intermittently and preferably continuously within at least one pressure reservoir, preferably within a plurality of pressure reservoirs, and preferably within all pressure reservoirs. Particularly preferably, these pressures are also used for the controller of the respective times or periods for the application of the flowable medium to the plastic preforms and/or for the return of the flowable medium (i.e., particularly the recycling) to the pressure reservoir(s).

Preferably, a first pressure or pressure stage is less than 12 bar, preferably less than 10 bar, more preferably less than 8 bar, and most preferably less than 6 bar.

Preferably, a first pressure or pressure level is greater than 2 bar, preferably greater than 3 bar, and more preferably greater than 4 bar.

The apparatus or method described herein is based on different approaches to optimize compressed air consumption.

In one method, the start times of the respective recycling branches, i.e., the times at which recycling occurs in the individual pressure reservoirs, are calculated as a function of the start times of the respective pressure stage in the pressurization phase. For example, it is possible for a start time for a pressure build-up and a start time for recycling to be determined in dependence on one another and, in particular, synchronized with one another. In this manner, simultaneous withdrawal from and supply to the pressure reservoir are achieved. Preferably, the following relationship applies to the start time of recirculation or recycling at a determined pressure level:Start time recycling=Start time pressure build-up

The factor A is calculated from 3600/the station output [b/h/c] (bottles per hour per cavity) and/the number of stations. The variable n depends on different quality parameters of the container, for example a pressure holding time of the highest level and is therefore also dependent on the customer object. The variable n is preferably calculated depending on these operator inputs. The variable n is an integer multiple (1, 2, 3, . . . ).

In a further method, the difference in pressure levels resulting for the respective pressure stage during pressure build-up and recycling is controlled and, in particular, regulated to a minimum. For this purpose, the pressure build-up and recycling or the pressures occurring there are measured. A valve opening time of the individual intermediate blowing pressure stages, particularly during the pressure build-up phase, is preferably used as the nominal variable for this control.

The starting pressure levels can be preset, for example by a machine operator, but they can also be preset by a machine controller or calculated or adjusted by means of artificial intelligence.

In a further preferred method, these starting pressure levels are preset or specified by a—preferably automated—calculation method. Subsequently, the fresh air replenishment is preferably deactivated. The pressure reservoirs can be filled exclusively by recycled air. The pressure levels in the pressure reservoirs preferentially set themselves based on the conditions of the physical system.

Preferably, for at least one pressure reservoir, the supply of fresh air is at least temporarily interrupted, particularly during normal operation of the apparatus.

The procedure described above is preferably first carried out individually for each individual pressure stage, and particularly preferably starting from the highest intermediate blowing pressure level to the lowest intermediate blowing pressure level. Subsequently, iterations of this procedure are preferred until the pressures in the pressure reservoirs do not change significantly over a certain number of iterations.

Preferably, the flowable medium is recirculated between a plurality of forming stations and the respective pressure reservoir, and preferably between all forming stations and the respective pressure reservoir (and preferably a plurality of pressure reservoirs).

Preferably, the return between the individual stations is staggered.

Particularly preferably, a value is determined taking into account an expansion pressure (i.e., the pressure when the plastic preform is acted upon) and the recycling pressure (i.e., the pressure that is present at the start time of the recycling) and, in particular, a comparison value is determined taking into account the expansion pressure and the recycling pressure, and, particularly preferably, this second value (in particular a start time for the recycling or the recycling of the flowable medium) is determined taking into account this comparison value. It is possible to measure this comparison value, particularly by means of two or more sensor devices, but the comparison value can also be determined from a blowing curve. This comparison value can be used as a controlled variable for a controller which regulates the start time for the recirculation of the flowable medium.

In a further preferred method, the comparison value is a difference and/or a quotient of the expansion pressure and the recycling pressure, and preferably the second value is controlled such that this comparison value becomes minimal. For example, a difference between the expansion pressure and the recycling pressure can be determined and the latter can be controlled to a minimum (particularly by means of changing the start time for recycling).

The same would be possible with a quotient. Also, a certain factor can be set in the calculation, which is determined by a user, for example. Thus, it is possible for the control to take into account whether or not this comparison value falls below a determined limit value. Accordingly, an adjustment can be made.

In a further preferred method, at least one valve opening time is changed for control, and preferably multiple valve opening times are changed. Particularly preferably, at least one valve opening time of a valve controlling an intermediate pressure stage (Pi and/or Pi+) is changed. Particularly preferably, a plurality of valve opening times are changed and, in particular, valve opening times of those valves which are responsible for supplying different intermediate blowing pressure stages. In another preferred method, the control or adjustment to a certain minimum of the pressure differences is done iteratively.

Particularly preferably, the method is performed for several pressure stages and/or several pressure reservoirs, and particularly preferably, this method is first performed for a higher pressure stage and subsequently for a lower pressure stage.

In a further preferred method, at least one time and/or time period for a return to the first pressure reservoir is determined as a function of a time and/or time period that is characteristic of the application of pressure from the first pressure reservoir to the plastic preforms.

Similarly, it is also possible to determine a time and/or period for a return to the second pressure reservoir as a function of a time and/or period characteristic of the application of pressure from the second pressure reservoir to the plastic preform.

In a further preferred method, in order to determine the time and/or time period for the return to the first pressure reservoir, at least one parameter is taken into account which is characteristic for the container to be expanded and/or for a time period of the application of a further pressure level.

In particular, the start times for a return to the first pressure reservoir and/or to the second pressure reservoir are determined in this mentioned manner. As an alternative to determining the respective time, it would also be possible to determine the time indirectly, for example via a position of the forming station along its transport path. As mentioned above, the forming stations are preferably transported on a rotatable carrier such as a blowing wheel. Thus, it would be possible to start returning the flowable medium to the respective pressure reservoir, at a predetermined position of the forming station along the transport path.